wgl: Call flush_resource() before presenting

Reviewed-by: Charmaine Lee <charmainel@vmware.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7535>

src/gallium/frontends/wgl/stw_st.c

@@ -267,6 +267,9 @@ notify_before_flush_cb(void* _args)
 
       /* FRONT_LEFT is resolved in flush_frontbuffer. */
    }
+
+   if (args->stwfb->textures[ST_ATTACHMENT_BACK_LEFT])
+      pipe->flush_resource(pipe, args->stwfb->textures[ST_ATTACHMENT_BACK_LEFT]);
 }
 
 void
@@ -335,6 +338,9 @@ stw_st_framebuffer_flush_front(struct st_context_iface *stctx,
       stw_pipe_blit(pipe, stwfb->textures[statt], stwfb->msaa_textures[statt]);
    }
 
+   if (stwfb->textures[statt])
+      pipe->flush_resource(pipe, stwfb->textures[statt]);
+
    pipe->flush(pipe, NULL, 0);
 
    /* We must not cache HDCs anywhere, as they can be invalidated by the